A few things come to mind here. When you swapped the dodge 60 in did you use the offset shackles to mount it? The dodge 60’s sit on a slightly narrower perch width than the GM 60’s. If you didn’t use them I wonder if there’s something there.
Also you mentioned the spring bushings being new, what kind did you use? Did you replace the actual king pins themselves in all this? Shackle hanger bushings new too? Shackle hangers themselves not worn out? (Mine were) Bolt holes in front hangers not wallered out? (Mine were) Same with shackle holes? How about your toe, where is it set? I suspect you’ve got a bigger issue than king pin issues and you are only masking the problems by focusing on just the king pins and really obvious stuff like the rod ends. Is your truck stock height? What condition are the springs and shocks in? How is your steering box, and it’s mounting holes in the frame? Any cracks around the steering box mounts? these trucks are notorious for that. Basically any loose part or combination of loose/worn parts/mounting holes can cause death wobble. Improper toe can be a big cause and wrong air pressures can even contribute. Lots of things to look over for sure. I’ll add a link to said conversion shackles.
https://www.offroaddesign.com/hd-fro...-hanger-1.html